There has recently been a strong need for a method for forming an image on a substrate of a color other than white, for example, a transparent or translucent film, or colored paper in a commercial printing market. When an image is formed on any of these substrates of a color other than white, a white image needs to be formed.
A method in which a film is formed on a substrate with a white ink containing white pigment particles dispersed therein is known as one of the methods of forming white images. Generally, metal oxide particles such as titanium oxide particles are often used as white pigment particles. Because the metal oxide particles have high densities, when a white ink containing the metal oxide particles dispersed therein is allowed to stand in an ink tank, the particles are settled with time. When the particles are settled in the ink tank, a film to be formed can have nonuniformity, and, furthermore, a nozzle can be clogged. Thus, the ink in the ink tank needs to be circulated or agitated at regular intervals.
Japanese Patent Laid-Open No. 2014-95058 discloses a white ink containing titanium oxide particles having a small particle size and hollow resin particles having a low specific gravity in order to inhibit settling of the particles in an ink tank.